Various types of engines produce vibration due to any unbalanced forces in their design. For example, such vibration may be generated because of the reciprocating motion of the connecting rods and pistons. In particular, during a given period of crankshaft rotation, descending and ascending pistons may not be completely opposed in their acceleration, giving rise to a net inertial force that creates an unbalanced vibration. Such vibration may reduce the drivability of a vehicle and may be negatively perceived by a vehicle operator.
In one example, an engine may include a balance shaft system that includes counter-rotating balance shafts. The balance shafts may have counterweights that are sized and phased so that the inertial reaction to their counter-rotation provides a net force equal to but opposing the undesired vibration of the engine, thereby canceling it. However, the inventors herein have recognized issues with the above approach.
For example, the balance shaft system may add cost and weight to the engine. Moreover, operation of the balance shafts system may cause friction losses that negatively impact engine power and fuel economy.
Thus, in one example, the above issues may be addressed by an engine comprising: a piston operable to reciprocate in a cylinder, a crankshaft rotatably coupled to the piston, and a supercharger rotatably coupled to the crankshaft, the supercharger having an unequal distribution of mass along a longitudinal plane of the supercharger to provide a rotational counterbalance to reduce the inherent engine unbalance.
In one example, the supercharger includes two counter-rotating rotors arranged in the longitudinal plane of the supercharger to increase intake air charge pressure provided to the cylinder. One or both of the rotors may be configured such their mass is unequally distributed to provide a rotational counterbalance or rotation couple that opposes vibration of the engine. In this way, engine vibration may be reduced without the use of a separate balance shaft system. By adding balancing functionality to the supercharger weight, cost, friction, and package space of the engine may be reduced relative to an engine that employs a balance shaft system.
Moreover, the supercharger may be mounted to the engine in different locations with the rotors parallel to the crankshaft, yet still provide the rotational counterbalance to reduce the inherent imbalance of the engine. In this way, the supercharger may provide greater engine packaging flexibility relative to a balance shaft system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.